Tube-in-shell heat exchangers

ABSTRACT

A tube-in-shell heat exchanger comprises co-axial tubes on the longitudinal axis of a bundle of heat exchange tubes. The outer tube incorporates two spaced cylindrical tube sheets in which the opposed ends of the heat exchange tubes are received. The outer tube is closed at one end and the corresponding end of the inner tube is sealed to the outer tube between the tube sheets to define discrete co-axial fluid flow ducts which are interconnected at the closed end region of the outer tube by the heat exchange tubes.

United States Patent Richardson 1 Sept. 30, 1975 [54] TUBE'INSHELL HEAT EXCHANGERS FOREIGN PATENTS OR APPLICATIONS [751 memo Richards wdmngmm 1.332.116 6/1963 France 122 32 England [73] Assignee: United Kingdom Atomic Energy Primary E\'uminer-Charlcs J. Myhrc Authority. London England Asxismn! ExuminerTheophil W. Strculc, .Ir. I ,.I:'. H' 1 filed: Mar 1974 411mm Agent or um L irSon Tiylor & 1ndS 211 Appl. No.2 456,265 [57] ABSTRACT A tubc-in-Shell heat exchanger comprises co-uxial {30] Forelgn Apphfanonrnonu Data tubes on the longitudinal axis of a bundle of heat cx- Apr. 16. 1973 United Kingdom 18312/73 Change tubes The Outer tube incorporates two spaccd cylindrical tube sheets in which the opposed ends of U.S- Cl- 1 the heat exchange tubes arc reccivcd The uter tube 51 Int. Cl F28f 9/02 is Closed at one end and the Corresponding end of the 8] Fleld of Search l65/l58l6l, inner tube is Sealed to the Outer tube between the tube 165/145; 122/32, 3 1 76 sheets to define discrete co-uxiul fluid flow ducts which are interconnected at the closed end region of [561 References C'ted the outer tube by the heat exchange tubes.

UNITED STATES PATENTS 5 Cl 2 D 3.768.554 10/1973 Smhl 165/159 ramng U.S Patent Sept. 30,1975 Sheet 1 of2 3,908,756

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TUBE-IN-SHELL HEAT EXCHANGERS BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS In the tube-in-shell heat exchanger shown in the This invention relates to tube-in-shell heat exchangdrawing a bundle of Parallel heat exchange is ers.

In general. tube-in-shell heat exchangers comprise a bundle of parallel tubes within a shell or container, one fluid being arranged to flow through the tubes in heat exchange with a second fluid flowing through the shell. The tubes are usually end supported by tube plates or sheets which separate the two fluids and in use the tube attachments and tube plates can be subject to severe stress by thermal shock. Therefore, frequent inspection and servicing may be required. In some heat exchanger applications, for example those wherein the heat exchangers are immersed in a nuclear reactor coolant such as liquid sodium, the inspection and servicing of tubes and tube plates is difficult to accomplish.

SUMMARY OF THE INVENTION In a tube-in-shell heat exchanger according to the invention the opposed ends of the heat exchange tubes are attached to the wall of a longitudinally extending central tube member, the attachments of the opposed ends of the tubes being arranged in two discrete groups spaced apart along the longitudinal axis of the tube member, and within the tube member there is a demountable tubular baffle which seals against the wall of the tube member between the groups of tube end attachments to define two discrete co-axial flow ducts, the ducts being interconnected at a closed end region of the tube member by the heat exchange tubes. In a heat exchanger according to the invention the demountable baffle can be removed to enable insertion of equipment for inspecting the wall of the tube member and tube attachments and to facilitate plugging of defective tubes.

In a preferred construction of heat exchanger the tube member incorporates cylindrical tube sheets in which the ends of the tubes are received. Cylindrical tube sheets are believed to be superior to tube plates for carrying pressure loads and resisting the effects of thermal shock. Because the tensile stress created by pressure in the cylindrical tube sheet is spread over the full wall thickness. the wall may be relatively thin whereas in the flat tube plate normally associated with conventional heat exchangers the more complex stresses created by bending necessitate a relatively thick wall. Some protection against thermal shock for a heat exchanger according to the invention can be effected by arranging that the secondary heat exchange fluid (fluid of least temperature) is on the tube side and by providing a thermal baffle to prevent direct impingement of hot primary fluid onto the cylindrical tube sheets.

DESCRIPTION OF THE DRAWINGS A construction of heat exchanger in accordance with the invention for use in a liquid sodium environment will now be described by way of example with reference to the accompanying fragmentary diagrammatic drawings FIGS. 1 and 2 which together present a sectional view.

ignated 1 and the shell 2. There is a central thimble shaped tube member 3 to which the ends of the tubes la are attachedv The opposed ends of the tubes 1a are arranged in two discrete groups spaced along the longitudinal axis of the tube member 3 and the tubes are adapted for attachment thereto by cylindrical tube sheets 4 which are incorporated in the tube member; the tubes Ia are bore welded into the tube sheets 4 by the tungsten inert gas process to form crevice free welds. In the tube member 3 there is a demountable tubular baffle 5 which seals against the wall of the tube member between the groups of the tube end attachments to define two discrete co-axial coolant flow ducts 6 and 7. The co-axial coolant flow ducts 6 and 7 are interconnected by the heat exchange tubes la. The tubular baffle 5 is double walled to define an argon filled interspace for reducing heat transfer through the baffle and there is a flexible expansible region 5a in the inner wall to prevent distortion of the baffle by differential thermal expansion of the two walls. A cylindrical baffle 8 is provided to prevent direct impingement of primary coolant fluid on the tube member 3 and tube sheets 4 and thereby attentuate thermal shock.

In use, primary coolant fluid flows vertically downwardly through the shell 2 over the tube bundle. The secondary fluid flows downwardly through the duct 6 of the baffle 5 thence upwardly through the heat exchange tubes la and the outer duct 7. By removing the demountable baffle 5 access can be gained to the tube member for inspection of welds and if necessary for plugging any defective tubes.

In greater detail, the heat exchanger is arranged to depend from the roof (designated 9) of the vault of a nuclear reactor construction. The vault contains the reactor core submerged in liquid sodium at approximately 600C and the heat exchanger is immersed in the sodium the level of the sodium being designated L in the drawing. The exchanger has a housing lO (shown in broken line) which has an inlet port 11 formed by a horizontal duct 12 for primary sodium and an outlet port 13 in the base region. An internal plenum 14 for distributing primary fluid flow uniformly around the heat exchanger is bounded by the baffle 8 and a perforated baffle 15. A perforated horizontal grid plate 16 effects a unform flow profile to the tube bundle. After flowing downwardly through the tube bundle the primary fluid enters a discharge plenum 17 which is arranged to pass some flow into the upper regions of the pool of sodium and the remainder to mix in the lower pool regions. A further grid assembly 18 is provided above the inlet port level to reduce flow turbulence within the plenum 14'. such flow turbulence causes surface disturbance which induces gas entrainment in the sodium. A cylindrical sleeve 19 vertically slidable in the shell is actuated from above the roof of the vault to provide cut-off and coarse flow control by variably obturating the inlet port 11. Heat exchange coils 20 are for use when the reactor has become inoperative to remove decay heat to outside the vault. Inlet and outlet ports 21, 22 for the secondary sodium are located above the roof 9 of the vault. A drain tube 23 extends from the base within the tube member 3 to a drain facility situated between two spaced annular seals 24, 25 which close the upper end of the duct 7. Sodium can be discharged from the tube member 3 by way of the drain tube 23 and drain facility by pressurising the upper regions with argon gas. The tube member 3 has a removable top cover 26 to enable the tubular baffle to be withdrawn into a flask and thus expose the internal wall of the cylindrical tube sheets 4 and the tube ends for inspection and repair by suitable equipment. Advantages derived from the invention in such a nuclear reactor application comprise:

a. the inside surface of the tubular member 3 can be visually inspected by television camera or endoscope,

b. crack development can be detected by stress wave emission,

c. tube wall thickness can be inspected by eddy current techniques,

d. tubes can be examined for leakages by temporarily plugging tube ends and checking for depressurisation. and

e. defective tubes can be closed by plug welding both ends.

Such techniques are carried out in an argon/sodium vapour environment at approximately 200C.

In an alternative construction the heat exchange tubes are of helical form. Exchangers having helically wound tubes have the advantage that a smaller number of tubes are required to achieve the desired heat transfer rate but they have the disadvantage that the secondary fluid flow is subject to high pressure drop.

I claim:

1. A tube-in-shell heat exchanger comprising.

a bundle of parallel heat exchange tubes within a shell and having their ends received in a pair oflongitudinal spaced cylindrical tube sheets,

a tube member disposed on the longitudinal axis of the bundle of tubes. the tube member incorporating the spaced tube sheets and having a closed end.

a demountable tubular baffle disposed within the tube member and sealed thereto between the tube sheets to define discrete co-axial fluid flow ducts interconnected at the closed end region of the tubular member by the heat exchange tubes.

2. A heat exchanger according to claim 1 wherein the tubular baffle comprises inner and outer spaced walls, the interspace containing argon and the inner wall having a flexible expansible region.

3. A heat exchanger according to claim 2 having a cylindrical baffle spaced from and encircling the tube member and tube sheets.

4. A heat exchanger according to claim 2 in which the shell has at least one radial inlet port for heat exchange fluid flow and a closure member for the port comprising a cylindrical sleeve slidable along the longitudinal axis of the shell.

5. A heat exchanger according to claim 2 having a drain tube extending within the tube member from the closed end to a drain facility in the opposed end region of the tube member.

i l l 

1. A tube-in-shell heat exchanger comprising, a bundle of parallel heat exchange tubes within a shell and having their ends received in a pair of longitudinal spaced cylindrical tube sheets, a tube member disposed on the longitudinal axis of the bundle of tubes, the tube member incorporating the spaced tube sheets and having a closed end, a demountable tubular baffle disposed within the tube member and sealed thereto between the tube sheets to define discrete coaxial fluid flow ducts interconnected at the closed end region of the tubular member by the heat exchange tubes.
 2. A heat exchanger according to claim 1 wherein the tubular baffle comprises inner and outer spaced walls, the interspace containing argon and the inner wall having a flexible expansible region.
 3. A heat exchanger according to claim 2 having a cylindrical baffle spaced from and encircling the tube member and tube sheets.
 4. A heat exchanger according to claim 2 in which the shell has at least one radial inlet port for heat exchange fluid flow and a closure member for the port comprising a cylindrical sleeve slidable along the longitudinal axis of the shell.
 5. A heat exchanger according to claim 2 having a drain tube extending within the tube member from the closed end to a drain facility in the opposed end region of the tube member. 